WASHINGTON — Chuck Hagel has been held up en route to his new job as the Pentagon's top boss.

In an unprecedented move, Senate Republicans are filibustering a vote to confirm President Barack Obama's pick as the next defence secretary.

It's the first time a defence secretary nominee has been filibustered, and only the third time in recent history any presidential nominee has been delayed by the opposition.

But the GOP, still trying to put the screws to the White House over the Sept. 11 terrorist attack in Benghazi last fall, are demanding answers from the administration.

(Democrats have 55 of the Senate's 100 seats, which is enough to confirm Hagel, but 60 votes are required to break the filibuster and hold a simple majority vote.)

"The president has a right to appoint people in whom he has confidence, but we have a constitutional responsibility to consider the nominee," said Tennessee. Republican Sen. Lamar Alexander on the floor Thursday night. "(And) a number of the Republican senators have questions."

Congress is in recess next week, and many Republicans have suggested they'll be prepared to allow a vote on Hagel after the break.

But the White House is livid and are accusing Republicans are putting, "political posturing ahead of national security," according to chief spokesman Jay Carney.

Outgoing Defence Secretary Leon Panetta, who was hoping to retire Friday, has agreed to stay on until Hagel is sworn in.

The next vote in the Senate to break the Republican filibuster is set for Feb. 26.